By calculating fractal intercept of fracture surface of 10 concrete samples and 37 selected randomly section lines,the inherent defect of fractal intercept in characterizing waviness-insensitivity to change of waviness is analyzed. This limitation easily results in experimental result inconsistent with theory in experimental study. Thus,an assumption of substituting fractal intercept with average angle of surface ( on the condition of studying surface) or average angle of curve ( on the condition of studying curve) in experimental study was put forward. Average angle of surface or average angle of curve not only better describes waviness characteristic of surface or curve,but also effectively overcomes the disadvantage of fractal intercept in describing waviness. In this paper,the function relation between above two kinds of average angles and fractal intercept is discussed,and it is pointed out that the two function relations can be unified in form of A = αLnθ + β.